The charted channel depth at Eastport, ME, is 28 feet. You are drawing 31.5 feet and wish 2 feet clearance under the keel. What is the earliest time after 1700 (ZD +4) on 6 September 1983 that you can enter the channel?
• Chart datum and soundings (charted depth is usually at Mean Low Water) • Required clearance: combine vessel draft and desired under-keel clearance to get minimum total depth needed • Tide tables for Eastport, ME on 6 September 1983 and how to find water height at specific times
• How do you convert the vessel’s draft and desired under-keel clearance into a minimum water depth you must have? • Given the charted depth, how much tide height above datum is needed to safely enter? • Looking at the tide table for Eastport on 6 Sept 1983, during the period after 1700, when does the predicted tide height first become equal to or greater than that required height?
• Compute minimum depth = draft + desired clearance (in feet) before you look at the choices • Compute required tide height = minimum depth − charted depth (in feet) and keep that number in mind • Use the tide curve or table values for the evening tide on 6 Sept 1983 at Eastport to find the first time after 1700 when the tide height is at least that required value, then match that time to the closest choice.
No comments yet
Be the first to share your thoughts!